This invention arose as a result of attempts to improve upon conventional hand guiding techniques in the use of portable electric drills in industry, commercial construction and fabrication as well as "do-it-yourself" home projects and home workshop operations. Skilled craftsmen as well as amateurs often have a need to bore accurately perpendicular holes in a workpiece. It is well known in the art that holes cannot be bored with any appreciable degree of perpendicular precision With a hand supported power drill because of the inherent human error in maintaining the drill in a true perpendicular relationship with the workpiece
While various drilling guides are on the market, they do not, to my knowledge, utilize the drill housing itself as a means to guide the drill as set out herein. Several devices such as the portalign Drill Guide, U.S. Pat. No. 3,874,810, and the Precision Drill Guide, Pat. Applied For, are effective for their dedicated purposes but do share draw-backs in common including inconvenience involved in preparing the drill guide for use as well as comparatively high cost of the product.
Both these devices necessitate removal of the chuck from the drill to allow reassembly on the drill guide's shaft. The drill is then threaded to the end of the drill guide's spindle. These temporary switch-overs take time, thus often discouraging utilization, particularly for minor drilling operations. Optionally, an auxiliary chuck and adapter may be permanently installed on the guide to avoid the need for removal from the drill. This adds more to the cost.
Less sophisticated drill guides, also on the market, utilize short bushings which are meant to support the drill perpendicularly. Accuracy of the drilled holes is not assured with such bushing type guides inasmuch as guidance relies upon the thrust of the side of the drill bit against the comparatively small wall of the bushing. Thus, lacking ample flanking support of the bulk of the tool in the area away from the bushing, the hand holding and driving the drill is prone to sway or drift off the intended true perpendicular axis The result is a non-perpendicular drilled hole. Also, the top of the bushing or its holder acts as an inadvertent stop against the drill chuck thus limiting the travel of the drill bit. This appreciably limits the depth of hole that could otherwise be achieved.